Peter Askin’s movie about the left-wing Hollywood screenwriter Dalton Trumbo is fine when it’s in standard-bio-documentary mode, offering the fascinating life of the famously combative scripter who as a member of the Hollywood Ten was blacklisted and jailed in the 1950s for contempt of Congress, and who signed letters, “Irritably yours.” Not so gratifying are the artsy, self-conscious snippets from the stage play Trumbo penned by his son, Christopher Trumbo. Dalton’s rhetorical letters are read by a host of worshipful, overacting “A”-list thespians — Joan Allen, Michael Douglas, Paul Giamatti, etc. The result is an epistolary embarrassment. 96 minutes | Kendall Square